In response to the increasing seriousness of global environmental issues, energy issues and the like, a solar cell is attracting attention as clean energy-generating means with no concern over depletion. In a case in which a solar cell is used outdoors such as on the roof of a building, it is usual to use the solar cell in a solar cell module form.
Generally, the solar cell module is manufactured in the following order. First, a crystalline solar cell element (hereinafter also referred to as a power generation element or a cell in some cases which indicates the same thing) formed of polycrystalline silicon or monocrystalline silicon, or a thin film-type solar cell element obtained by forming an extremely thin (several micrometers) film of amorphous silicon or crystal silicon on a glass substrate or the like is manufactured. Next, to obtain a crystalline solar cell module, a protective sheet (a transparent surface protective member) for the solar cell module, an encapsulating material for solar cell, the crystalline solar cell element, an encapsulating material for solar cell, and a protective sheet (a back surface protective member) for the solar cell module are sequentially laminated. Meanwhile, to obtain a thin film-based solar cell module, a thin film-type solar cell element, an encapsulating material for solar cell, and a protective sheet (a back surface protective member) for the solar cell module are sequentially laminated. After that, the solar cell module is manufactured using a lamination method or the like in which the above-described laminate is suctioned in a vacuum, heated and pressed. The solar cell module manufactured in the above-described manner is weather resistant and is also suitable for outdoor use such as on the roof of a building.
An ethylene/vinyl acetate (EVA) copolymer film is widely used as an encapsulating material for solar cell due to its excellent transparency, flexibility, adhesiveness and the like.
Patent Document 1 (Japanese Examined Patent Publication No. 6-35575) describes a composition for encapsulation which encapsulates an electronic material obtained by mixing an organic peroxide or a photosensitizer and a silane coupling agent with EVA as a composition for encapsulation. Furthermore, Patent Document 1 discloses that (meth)acrylic acid ester and/or an allyl group-containing compound may be mixed.
In addition, Patent Document 2 (Japanese Unexamined Patent Publication No. 2007-123488) discloses an adhesive sheet for solar cell containing an organic peroxide and a polyfunctional monomer having a total of four or more of any one or both of an acryloyl group and a methacryloyl group in EVA.
In contrast to what has been described above, recently, there have been active studies regarding polyolefin-based materials, and there is another proposal of a resin composition for an encapsulating material for solar cell for which an ethylene/α-olefin copolymer having an excellent balance between stiffness and crosslinking characteristics and extrusion moldability is used (for example, refer to Patent Document 3).